Current commercial jetliners with cargo compartments have built-in fire extinguishers and use bromotrifluoromethane as the extinguishant. It is sold commercially as Halon 1301. The current systems typically consist of a minimum of two separate Halon bottles, each with its own discharge mechanism. In the event of a cargo fire, fire suppression is achieved by rapid discharge of a first bottle to ensure a minimum compartment Halon concentration of 5% by volume for initial flame knockdown. Effective fire suppression against deep-seated fire continues as long as the Halon concentration remains above 3% by volume. In order to extend a desired fire suppression time, the second Halon bottle is timed to be discharged when the compartment Halon concentration decreases to 3%. This sequence of discharge can be performed for any number of Halon bottles to achieve any desired duration of fire suppression.
This method cannot optimize Halon utilization when long suppression times are required because leakage at high initial Halon concentration is characteristic after each subsequent bottle discharge.
A search of the patent literature discloses a number of fire extinguishing systems. For example, U.S. Pat. No. 3,783,946 uses an extinguishant open or shut control valve 20 and has wide open discharges 18 of the same size as the flow lines 16. This system permits a transient phase change of the extinguishant from liquid to gas unpredictably somewhere in the line distribution network, depending on the environment temperature to which the system is exposed. The result is an unsteady-state flow which cannot be accurately controlled as the extinguishant is changed into a gas phase. The gas thus is introduced at very low flows into the compartment and sinks locally to the bottom of the compartment because it is five times heavier than air. As a result, the mixing of the extinguishant in the compartment is likely to be incomplete and the fire suppression is not likely to be as effective as it should be.
The following patents disclose other fire extinguishing systems of general interest: U.S. Pat. No. 2,566,235, issued Aug. 28, 1951 to A. Mathisen; U.S. Pat. No. 2,601,900, issued July 1, 1951 to C. H. Rand et al.; U.S. Pat. No. 2,990,886, issued July 4, 1961 to G. A. Dean; U.S. Pat. No. 3,524,506, issued Aug. 18, 1970 to C. A. Weise; U.S. Pat. No. 3,642,071, issued Feb. 15, 1972 to Utesch, Jr.; U.S. Pat. No. 3,917,001, issued Nov. 4, 1975 to Davis et al; U.S. Pat. No. 4,101,887, issued July 18, 1978 to Osborne; U.S. Pat. No. 4,194,571, issued Mar. 25, 1980 to Monte; and U.S. Pat. No. 4,263,971, issued Apr. 28, 1981 to Spector et al.